Communication method, communication device, and computer program

ABSTRACT

In order to solve a problem of an accumulation on the transmission side, a delay on the reception side, and the like at the time of transmission in a communication system such as a wireless LAN system, each communication station in a network transmits a beacon in which information with respect to the network is written and sets a state in which a reception operation is performed during periods of time before and after the transmission of the beacon signal when performing access control not to make communication timing of a packet collide with that of another station by detecting a signal transmitted from another station. With performing such processing, a system can be formed based on minimum level of transmission and reception operation when transmission and reception data does not exist in each communication station in the network, and also a data transfer can be performed with latency as small as possible in a minimum necessary level of transmission and reception operation by making a transition of a transmission and reception state in accordance with a fluctuating volume of transmission and reception data.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/733,226, filed Apr. 10, 2007, which is a continuation of and is basedupon and, under 35 U.S.C. §120, claims the benefit of priority of U.S.application Ser. No. 10/544,107 filed May 24, 2006, which is a NationalStage of PCT/JP04/01027, filed on Feb. 3, 2004, all of which claimpriority to Japanese Patent Application No. 2003-026462, filed on Feb.3, 2003. The contents of each of all of the above-identified documentsare incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a communication method and acommunication apparatus suitable for applying to a wireless LAN (LocalArea Network: local information and communication network) system whichperforms data communication and the like, for example. Particularly, thepresent invention relates to a communication method and a communicationapparatus suitable for applying to a case where an autonomousdistributed type network not having a controlling and controlledrelation between a master station and a slave station is operatedwithout a configuration control station.

In more detail, the present invention relates to a wirelesscommunication method and a wireless communication apparatus, as well asa computer program, in which an autonomous distributed type wirelessnetwork is formed in such a manner that each communication stationinforms mutually of a beacon having network information and the likewritten therein at a predetermined frame cycle, and particularly relatesto a wireless communication method and a wireless communicationapparatus, as well as a computer program in which an autonomousdistributed type wireless network is formed while each communicationstation avoids collision of beacons that are mutually transmitted.

BACKGROUND ART

In the past, an access control defined conforming to the IEEE (TheInstitute of Electrical and Electronic Engineers) 802.11 method, and thelike, are widely known as medium access control of a wireless LANsystem. Details of the IEEE 802.11 method is described in theInternational Standard ISO/IEC 8802-11:1999(E) ANSI/IEEE Std 802.11,1999 Edition, Part 11: Wireless LAN Medium Access Control (MAC) andPhysical Layer (PHY) Specifications, and the like. Networking in theIEEE 802.11 method is based on a concept of BSS (Basic Service Set).There are two kinds of BSS, a BSS defined by an infrastructure mode inwhich there exists a master control station such as an access point: AP,and an IBSS (Independent BSS) defined by an ad hoc mode which includesonly a plurality of terminal stations: MT (Mobile Terminals).

An operation in the IEEE 802.11 at the time of the infrastructure modeis explained using FIG. 27. In the BSS of the infrastructure mode, thereexists an access point performing coordination in a wirelesscommunication system, and communication is performed between the accesspoint and a terminal station MT existing around this access point. Theaccess point transmits a control signal called a beacon at anappropriate time interval, and a terminal station MT capable ofreceiving this beacon recognizes that the access point exists in theneighborhood and further establishes a connection with this accesspoint. FIGS. 27A to 27C describes a case where a communication stationSTA1 shown in FIG. 27A is an access point and a communication stationSTA0 shown in FIG. 27B is a terminal station MT. The communicationstation STA1 transmits a beacon at a fixed time interval as shown inFIGS. 27A to 27C.

The transmission time of the next beacon is informed in the beacon by aparameter called target beacon transmission time (TBTT), and the accesspoint makes a beacon transmission procedure operated when the timebecomes the TBTT. In addition, since the neighboring terminal station MTis able to recognize the next beacon transmission time by receiving thebeacon and decoding an internal TBTT field thereof, there is also a casewhere power supply to a reception unit is turned off until a TBTT of thenext time or of multiple times ahead and the station MT enters into asleep state during a period of time considered to be not necessary tocommunicate with the access point (so-called intermittent receptionoperation). When information addressed to a specific communicationstation is contained in a beacon, a field conveying to the effectthereof to the concerned communication station is defined in the beacon,and the terminal station MT having received the beacon can know whetherat present the access point retains information addressed thereto.

In FIGS. 27A to 27C, a case where the communication station STA0receives a beacon of the communication station STA1 once every two timesis shown as an example. FIG. 27C shows a state of a reception unit inthe communication station STA0, in which a high level shows a stateduring reception operation and a low level shows a state duringsuspension of reception. The communication station STA0 operates thereception unit at a timing when the communication station STA1 transmitsa beacon B1-0. However, when the reception of the beacon is completed,the communication station STA0 stops the operation of the receptionunit, because there is no description in the beacon B1-0 thatinformation addressed thereto is included. The communication stationSTA0 does not operate the reception unit when a next beacon B1-1 istransmitted, and operates the reception unit aiming at the time when thenext beacon B1-2 after the beacon B1-1 is transmitted. In FIGS. 27A to27C, a case where it is informed in this beacon B1-2 that informationaddressed to the communication station STA0 is included is referred toas an example.

The communication station STA0, which has recognized by receiving thebeacon B1-2 that the information addressed thereto is included,transmits a PS-Poll packet in accordance with a predeterminedtransmission procedure in order to convey to the communication stationSTA1 that the information is recognized and the reception unit keepsoperating. The communication station STA1 having received the packettransmits an information packet addressed to the communication stationSTA0 in accordance with the predetermined transmission procedure afterrecognizing that the communication station STA0 has started an operationof a receiving device. When receiving the information packet withouterror, the communication station STA0 transmits an ACK as a receptionacknowledgement signal. Hereupon, information indicating that there isno more information included at present in the communication stationSTA1 is written in the information packet received by the communicationstation STA0, and the communication station STA0 having recognized theabove again stops operation of the reception unit and makes a transitionto the intermittent reception operation.

Further, when the access point transmits broadcast information, theaccess point performs countdown to decide when a broadcast message istransmitted in the future and informs the count value in a beacon. Forexample, when broadcast information is transmitted immediately after thebeacon B1-2 in FIGS. 27A to 27C, a count value 2 is written in thebeacon B1-0, a count value 1 is written in the beacon B1-1 and a countvalue 0 is written in a beacon B1-3, and without receiving a beaconsignal each time, a terminal station MT can receive the broadcastinformation by referring to the relevant count value and operating thereceiving device at a point of time when the count value becomes zero.

Next, an operation of the IEEE 802.11 at the time of an ad hoc mode isexplained using FIGS. 28A to 28C. In the IBSS of the ad hoc mode, aterminal station (communication station) MT autonomously defines theIBSS after a negotiation is performed among a plurality of communicationstations MT. When the IBSS is defined, a communication station groupsets a TBTT at a fixed interval after a negotiation. When recognizingthe TBTT by referring to an internal clock of its own, eachcommunication station MT transmits a beacon after a delay of random timein case that it is recognized that nobody has transmitted a beacon yet.In FIGS. 28A to 28C, a case where two MTs that are the communicationstation STA0 and the communication station STA1 form an IBSS is shown asan example. FIG. 28A shows a packet that the communication station STA1transmits and receives, FIG. 28B shows a packet that the communicationstation STA0 transmits and receives, and FIG. 28C shows an operationstate of the reception unit of the communication station STA0 (in astate of high level reception operation and in a state of low levelreception suspension). With respect to a beacon in this case, acommunication station MT of either the communication station STA0 or thecommunication station STA1, which belongs to the IBSS, transmits abeacon each time the TBTT has come.

In the IBSS, also there is a case in which a communication station MTturns off a power supply to a transmission-reception unit and enters asleep state depending on necessity. When a sleep mode is applied in theIBSS, a period of time for some time from the TBTT is defined as an ATIM(Announcement Traffic Indication Message) window in the IEEE 802.11. Allthe communication stations MT belonging to the IBSS operate receptionunits during the period of time of the ATIM window, and also acommunication station MT basically operating in the sleep mode iscapable of receiving during this period of time.

When each communication station MT retains information addressed toanother station, the fact that the station retains the informationaddressed to the above another station is notified to a receiving sideby transmitting an ATIM packet to the above-described another stationduring the period of time of the ATIM window after a beacon istransmitted. The communication station MT having received the ATIMpacket or the communication station MT having transmitted the beaconkeeps a reception unit operating until the next TBTT.

In FIGS. 28A to 28C, when it becomes the first TBTT, each communicationstation MT of the STA0 and STA1 operates a back-off timer whilemonitoring a state of the medium over a random time. A case in which atimer of the communication station STA0 finishes counting at theearliest and the communication station STA0 transmits a beacon is shownin an example of FIGS. 28A to 28C. Since the communication station STA0has transmitted a beacon, the communication station STA1 having receivedthis beacon does not transmit a beacon. Further, the communicationstation STA0 keeps the reception unit operating until the next beacon istransmitted, because the STA0 has transmitted the beacon.

At the next TBTT, the communication station STA1 transmits a beacon inaccordance with a procedure of random back-off. At this time, althoughthe communication station STA0 operates the reception unit during theperiod of time defined by the ATIM window, the station STA0 receives noinformation from another station during this period and thereby thecommunication station STA0 stops the reception unit immediately afterthe period of the ATIM window is over and makes a transition to a sleepstate until the next TBTT. Even at the next TBTT, the communicationstation STA1 transmits a beacon again in accordance with the procedureof random back-off. At this time, since the communication station STA0receives an ATIM message from the communication station STA1 whilekeeping the receiving device operating during the period of time definedby the ATIM window, the communication station STA0 keeps the receptionunit operating after the period of the ATIM window is over and receivesinformation transmitted from the communication station STA1. Since anACK that is a reception acknowledgement is received in response to theATIM message, the communication station STA1 tries to transmit a datapacket by activating the procedure of random back-off starting from apoint of time that the ATIM window is ended after confirming that thecommunication station STA0 recognizes the reception. After that, boththe communication stations STA1 and STA0 keep the reception unitsoperating until the next beacon transmission.

As described above, in a wireless communication system (wireless LAN andthe like) of related art, a communication station which has noinformation to receive turns off a power supply to atransmission-reception unit until the next TBTT and can reduce powerconsumption.

An example of wireless communication processing in related art usingsuch beacon is disclosed in Published Japanese Patent Application No.H8-98255.

When the above communication control is performed, the followingproblems exist.

Accumulation of Data Occurring on Transmission Side

An appearance in which a packet transmission delay occurs in a system ofrelated art is shown in FIGS. 29A to 29E.

FIG. 29A is a packet sent from an upper layer of the communicationstation STA1, FIG. 29B is a packet (including a beacon) transmitted andreceived by a MAC layer of the communication station STA1, FIG. 29C is apacket transmitted and received by a MAC layer of the communicationstation STA1, and FIG. 29D is a packet received by the communicationstation STA1 and sent to an upper layer. In addition, FIG. 29E shows areception operation state in the reception unit of the communicationstation STA1. Once a reception unit is stopped, a communication stationdoes not operate the reception unit until the next beacon transmissiontime. Therefore, when data is transferred from the communication stationSTA1 to the communication station STA0 and in such a case thatinformation is periodically passed down from an upper layer of thecommunication station STA1, the next time when the communication stationSTA0 having made the reception unit once stopped operates the receptionunit is at the time when the communication station STA1 transmits abeacon, and data from D1 to D5 passed from an upper layer of thecommunication station STA1 during this period are accumulated within thecommunication station STA1 as shown in FIGS. 29A to 29E, for example.The accumulation of data within the transmission and reception unitcauses an increase (increase of latency) in round trip time (RTT)between the reception and transmission units at an application level,and there occurs a problem that throughput reaches a ceiling when ARQusing a sliding window is performed. Moreover, in order to avoid anoverflow, a buffer as big as one capable of sustaining the dataaccumulation within the communication station STA1 that is thetransmission station is needed, which causes a problem of limitationregarding hardware.

Increase in Idle Reception Period Occurring on Reception Side

Next, an idle reception period that occurs on a reception side isexplained using FIGS. 30A to 30F. FIG. 30A through 30E are the same asFIGS. 29A through 29E, and FIG. 30F shows an idle period.

In addition, although a method of keeping a reception unit operatingeven after the reception of information is employed in related art inorder to solve the above-described problem, the reception unit becomesalways operating in this case as shown in FIGS. 30A to 30F, for example.Although the accumulation of data in the transmission station STA1 iscertainly resolved, the reception unit is uselessly operated in thecommunication station STA0 that is the reception side and a problemremains from a viewpoint of power consumption since there exist a numberof idle periods (period shown with an arrow in FIG. 30F) in which datareception is not performed actually though the reception unit keepsoperating.

Latency of Broadcast Information

Further, although broadcast information transmitted and received in aninfrastructure mode can be conveyed even if a communication station MTreceives beacon information only once in several times, it is necessaryto keep the transmission of the broadcast information waiting from thetime when data is passed from an upper layer until countdown is endedwhen an access point AP intends to broadcast the data passed from theupper layer, and there occurs such a problem that a delay until thebroadcast information is actually transmitted becomes large.

The present invention is made in view of those problems and aims atsolving problems such as accumulation on a transmission side and delayon a reception side at the time of transmission in a communicationsystem such as a wireless LAN system.

DISCLOSURE OF THE INVENTION

In the present invention, in communication performed in a networkincluding a plurality of communication stations, in which access controlis performed in order to make communication timing of a packet notcollide with that of another station by detecting a signal transmittedfrom another station, each communication station in the networktransmits a beacon in which information with respect to the network iswritten and sets a state where a reception operation is performed duringa period of time before and after the transmission of the beacon signal.

According to the present invention, when transmission and reception datadoes not exist in each communication station in the network, forexample, a system is formed based on a minimum transmission andreception operation, and data transfer can be performed with latency assmall as possible in a necessary minimum transmission and receptionoperation by making a transition of transmission and reception operationstate in accordance with fluctuating volume of transmission andreception data. Accordingly, it is possible to provide an excellentcommunication method and communication apparatus, as well as computerprogram.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram showing an example of arrangement ofcommunication apparatuses according to an embodiment of the presentinvention;

FIG. 2 is a block diagram showing an example of a configuration of acommunication apparatus according to an embodiment of the presentinvention;

FIG. 3 is a block diagram showing in detail an example of aconfiguration of a communication apparatus according to an embodiment ofthe present invention;

FIG. 4 is an explanatory diagram showing an example of a beacontransmission interval according to an embodiment of the presentinvention;

FIG. 5 is an explanatory diagram showing an example of beacontransmission timing according to an embodiment of the present invention;

FIG. 6 is an explanatory diagram showing part of information written ina beacon according to an embodiment of the present invention;

FIG. 7 is an explanatory diagram showing an example of a NBOI and NBAIprocessing procedure according to an embodiment of the presentinvention;

FIG. 8 is an explanatory diagram showing an example of a definition of atransmission disapproval period according to an embodiment of thepresent invention;

FIG. 9 is an explanatory diagram showing an example of a transmissionprioritized period according to an embodiment of the present invention;

FIG. 10 is an explanatory diagram showing an example of a structure of asuper frame according to an embodiment of the present invention;

FIG. 11 is a timing chart showing an example of a communication state ina communication station according to an embodiment of the presentinvention;

FIG. 12 is an explanatory diagram showing an example of a neighborstation list according to an embodiment of the present invention;

FIGS. 13A and 13B are explanatory diagrams showing an example oftransition of an activity level according to an embodiment of thepresent invention;

FIGS. 14A to 14D are timing charts showing an example of a transmissionand reception procedure at the active level 0 according to an embodimentof the present invention;

FIGS. 15A to 15D are timing charts showing an example of a transmissionand reception procedure at the active level 1 according to an embodimentof the present invention;

FIGS. 16A to 16D are timing charts showing an example of a transitionprocedure to the active level 2 according to an embodiment of thepresent invention;

FIGS. 17A to 17E are timing charts showing an example of a transmissionand reception procedure at the active level 2 according to an embodimentof the present invention;

FIGS. 18A to 18E are timing charts showing an example of a transitionprocedure to the active level 1 according to an embodiment of thepresent invention;

FIGS. 19A to 19E are timing charts showing an example of a transitionprocedure to the active level 3 according to an embodiment of thepresent invention;

FIGS. 20A to 20E are timing charts showing an example of a transitionprocedure to the active level 2 according to an embodiment of thepresent invention;

FIGS. 21A to 21C are explanatory diagrams showing an example of abroadcast signal transmission state according to an embodiment of thepresent invention;

FIG. 22 is an explanatory diagram showing an example of a transmissionand reception procedure of a broadcast signal according to an embodimentof the present invention;

FIG. 23 is an explanatory diagram showing a transition of a neighborstation list at the time of transmission and reception of a broadcastsignal according to an embodiment of the present invention;

FIG. 24 is an explanatory diagram showing part of information written ina beacon signal according to an embodiment of the present invention;

FIG. 25 is an explanatory diagram showing transaction of active levelupload according to an embodiment of the present invention;

FIG. 26 is an explanatory diagram showing transaction of active leveldownload according to an embodiment of the present invention;

FIGS. 27A to 27C are timing charts showing an example of a transmissionand reception state in an infrastructure mode of a wirelesscommunication system in related art;

FIGS. 28A to 28C are timing charts showing an example of a transmissionand reception state in an ad hoc mode of a wireless communication systemin related art;

FIGS. 29A to 29E are timing charts showing an example of a packettransmission delay in a wireless communication system in related art;and

FIGS. 30A to 30E are timing charts showing an example of reception idletime in a wireless communication system in related art.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention is explainedreferring to FIGS. 1 through 25.

In this embodiment, a wireless propagation path of communication isassumed, and in which a network is formed among a plurality of devicesusing a single transmission medium (not a case in which a link isseparated based on a frequency channel). However, even if a plurality offrequency channels exist as the transmission medium, a similar thing canbe said. In addition, store-and-forward type traffic is assumed as thecommunication in this embodiment and information is transferred by aunit of packet.

An example of arrangement of communication apparatuses constituting awireless communication system according to an embodiment of the presentinvention is shown in FIG. 1. In this wireless communication system, nospecific control station is disposed, each communication apparatusoperates in an autonomously distributed manner, and what is called an adhoc network is formed. This figure illustrates an appearance in whichcommunication apparatuses from #0 to #6 are distributed in the samespace.

Further, a communication range of each communication apparatus is shownby a broken line in this figure, and the range is defined not only as arange in which mutual communication is possible with other communicationapparatuses existing within the range, but also as a range in which asignal transmitted from each station interferes with each other.Specifically, the communication apparatus #0 exists in a range capableof communicating with the communication apparatuses #1 and #4 existingin the neighborhood, the communication apparatus #1 exists in a rangecapable of communicating with the communication apparatuses #0, #2 and#4 existing in the neighborhood, the communication apparatus #2 existsin a range capable of communicating with communication apparatuses #1,#3 and #6 existing in the neighborhood, the communication apparatus #3exists in a range capable of communicating with the communicationapparatus #2 existing in the neighborhood, the communication apparatus#4 exists in a range capable of communicating with the communicationapparatuses #0, #1 and #5 existing in the neighborhood, thecommunication apparatus #5 exists in a range capable of communicatingwith the communication apparatus #4 existing in the neighborhood, andthe communication apparatus #6 exists in a range capable ofcommunicating with the communication apparatus #2 existing in theneighborhood.

When the communication is performed between certain specificcommunication apparatuses, there exists such a communication terminal,what is called a hidden terminal, that can be heard by a communicationapparatus of one side which becomes a communication partner but can notbe heard by the other communication apparatus.

FIG. 2 is a block diagram showing an example of a configuration of awireless transmission and reception apparatus constituting acommunication station applied to the system of this embodiment. In thisexample, an antenna 1 is connected to a reception processing unit 3 anda transmission processing unit 4 through an antenna shared device 2, andthe reception processing unit 3 and the transmission processing unit 4are connected to a base-band unit 5. Various communication methods whichare applicable to, for example, a wireless LAN and which are suitablefor communication of a comparatively short range can be applied withrespect to a reception processing method in the reception processingunit 3 and a reception processing method in the transmission processingunit 4. Specifically, a UWB (Ultra Wideband) method, an OFDM (OrthogonalFrequency Division Multiplex) method, a CDMA (Code Division MultipleAccess) method, and the like can be applicable.

The base-band unit 5 includes an interface unit 6, a MAC (Media AccessControl) unit 7, a DLC (Data Link Control) unit 8, and the like, andprocessing in each layer in an access control method mounted on thiscommunication system is performed in respective processing units.

FIG. 3 shows in further detail a functional configuration of a wirelesscommunication apparatus which operates as a communication station in acommunication network according to an embodiment of the presentinvention. Under an autonomous distributed type communicationenvironment in which a control station is not disposed, the wirelesscommunication apparatus shown in this figure can form a network byefficiently performing a channel access within the same wireless systemwhile avoiding a collision.

As shown in the figure, a wireless communication apparatus 100 includesan interface 101, a data buffer 102, a central control unit 103, abeacon generation unit 104, a wireless transmission unit 106, a timingcontrol unit 107, an antenna 109, a wireless reception unit 110, abeacon analysis unit 112, and a information memory unit 113.

The interface 101 exchanges various information sets with an externaldevice (for example, a personal computer (not shown in the figure), andthe like) connected to the wireless communication apparatus 100.

The data buffer 102 is used to temporarily store data sent from aconnected device through the interface 101 and data received through awireless transmission path before sent through the interface 101.

The central control unit 103 unitarily performs a series of managementof information transmission and reception processing and access controlof the transmission path in the wireless communication apparatus 100.Operation control such as collision avoidance processing at the time ofbeacon collision, for example, is performed in the central control unit103.

The beacon generation unit 104 generates a beacon signal which isperiodically exchanged with a wireless communication apparatus existingin the neighborhood. In order for the wireless communication apparatus100 to operate the wireless network, a beacon transmission positionthereof, a beacon reception position from a neighboring station, and thelike are defined. The information is stored in the information memoryunit 113 and at the same time, is written in a beacon signal and awireless communication apparatus in the neighborhood is informedthereof. A structure of the beacon signal is described later on. Sincethe wireless communication apparatus 100 transmits a beacon at the headof a transmission frame cycle, the transmission frame cycle in a channelused by the wireless communication apparatus 100 is defined by a beaconinterval.

The wireless transmission unit 106 performs predetermined modulationprocessing in order to wirelessly transmit data and a beacon signaltemporarily stored in the data buffer 102. Further, the wirelessreception unit 110 performs reception processing of a signal such asinformation and a beacon, which is sent from another wirelesscommunication apparatus at the predetermined time.

Various communication methods which are applicable to a wireless LAN andwhich are suitable for communication of a comparatively short range, forexample, can be applied as a wireless transmission and reception methodin the wireless transmission unit 106 and in the wireless reception unit110. Specifically, the UWB (Ultra Wide Band) method, the OFMD(Orthogonal Frequency Division Multiplexing) method, the CDMA (CodeDivision Multiple Access) method, and the like can be employed.

The antenna 109 wirelessly transmits a signal addressed to anotherwireless communication apparatus on a predetermined frequency channel,or collects a signal sent from another wireless communication apparatus.In this embodiment, it is assumed that a single antenna is provided andtransmission and reception may not be performed together in parallel.

The timing control unit 107 performs control over timing to transmit andto receive a wireless signal. For example, own beacon transmissiontiming at the head of the transmission frame cycle, beacon receptiontiming from other communication apparatuses, data transmission timing toand data reception timing from another communication apparatus, scanoperation cycle, and the like are controlled.

The beacon analysis unit 112 analyzes the beacon signal received from aneighboring station and analyzes the existence of a wirelesscommunication apparatus in the neighborhood, and the like. For example,information such as reception timing of a beacon in a neighboringstation and neighboring beacon reception timing is stored in theinformation memory unit 113 as neighboring apparatus information.

The information memory unit 113 stores an execution procedure command(program in which a collision avoidance processing procedure and thelike are described) on a series of access control operation and the likewhich is executed in the central control unit 103, and also stores theneighboring apparatus information and the like obtained from the resultof analyzing the received beacon.

In the autonomous distributed type network according to this embodiment,each communication station informs beacon information at a predeterminedtime interval on a predetermined channel and thereby makes anothercommunication station existing in the neighborhood (specifically, withina communication range) know of the existence thereof and notifiesanother station of a network configuration. Hereupon, the beacontransmission cycle is defined as a super frame, and is assumed to be 80ms, for example.

A communication station newly entered detects that the communicationstation has entered a communication range while hearing a beacon signalfrom a neighboring station by a scan operation, and is able to know anetwork configuration by decoding information written in the beacon.Further, beacon transmission timing thereof is set to timing at which abeacon is not transmitted from a neighboring station while synchronizinggradually with reception timing of the beacon.

Next, communication processing operation performed in a wireless networkincluding a plurality of communication apparatuses according to thisembodiment is explained.

A wireless communication system assumed in this embodiment is an exampleof a case where each communication station transmits a beacon signal ata fixed time interval using a prepared transmission path and informsother communication stations of the presence thereof. Further,effectiveness expected in this embodiment is also efficient in awireless communication system in general which shares a transmissionpath by time division.

FIG. 4 shows an example of a beacon transmission interval in thewireless communication system of this embodiment. In the example of FIG.4, a case in which there exist four communication stations of STA0,STA1, STA2, and STA3 is referred to as an example. Each communicationstation participating in the network periodically transmits a beacon ata super frame interval in order to make the existence of thecommunication station known to the neighbors. Hereupon, it is assumedthat one cycle is 80 [msec], and hereinafter an explanation is madeusing a case in which the beacon is transmitted at every 80 [msec], butthe cycle is not necessarily limited to 80 [msec]. If informationtransmitted with the beacon is 100 bytes, time required for transmissionbecomes 18 [.mu.sec]. Since the transmission is performed once every 80[msec], a medium occupancy rate of the beacon for one communicationstation is 1/4444 which is sufficiently small. Since a beacon istransmitted even when a transmission signal has not reached a station,the beacon looks meaningless but does not become a big problem due to areason that the transmission time rate is 1/4444 and is sufficientlysmall.

Each communication station synchronizes gradually while receiving andconfirming a beacon transmitted from a communication station existing inthe neighborhood. When a communication station appears newly in thenetwork, the new communication station sets beacon transmission timingthereof to timing at which a beacon is not transmitted from acommunication station existing in the neighborhood. As described above,and also since the beacon transmission time of each communicationstation is offset against each other as shown in the figure, the beacontransmission timing thereof is controlled while receiving a neighboringbeacon such that beacon signals do not overlap with each other.

FIG. 5 shows an example of a configuration of beacon transmission timingthat can be disposed in a super frame. In the example shown in thisfigure, a lapse of time in the super frame made of 80 msec isillustrated like a clock in which a needle of hour hand moves clockwiseon a circular ring.

In the example shown in FIG. 5, positions 0 to F of total sixteen areformed as “slots” in which the time when the beacon transmission can beperformed, that is, the beacon transmission timing can be arranged. Asexplained by referring to FIG. 2, it is assumed that disposition of abeacon is performed in accordance with such an algorithm that beacontransmission timing of a newly entered station is sequentially set attiming approximately in the middle of a beacon interval which has beenset by an existing communication station. When Bmin is defined as 5 ms,the number of beacons that can be disposed are sixteen at maximum persuper frame. Specifically, the number of communication stations that canenter the network are sixteen at maximum.

Although not explicitly illustrated in FIGS. 4 and 5, each beacon istransmitted at a time intentionally having some time offset from theTBTT (Target Beacon Transmission Time) that is each beacon transmissiontime. This is called “TBTT offset”. A TBTT Offset Indicator Sequence(TOIS) field where the TBTT offset is set as described above is definedbeforehand. A beacon transmission offset value showing the amount ofintentional offset of transmission of a beacon at this time incomparison with the TBTT is written in the TOIS. In this embodiment, theTBTT offset value is determined by a pseudo-random number. Thispseudo-random number is determined by a pseudo-random sequence TOIS(TBTT Offset Indication Sequence) in which the number is uniquelydecided, and the TOIS is renewed in every super frame cycle.

By providing the TBTT offset, the actual beacon transmission time of twocommunication stations, even when two communication stations have beacontransmission timing disposed in the same slot on the super frame, can bemade to have an offset, and since each communication station canmutually hear each other's beacons in another super frame cycle (or, acommunication station existing in the neighborhood can hear both thebeacons) even if beacons collide with each other in a certain superframe cycle, the occurrence of collision of the beacon thereof can berecognized. A communication station informs a neighboring station of aTOI which is set in every super frame cycle and which is included inbeacon information.

Further, in this embodiment, each communication station is obliged toperform a reception operation before and after transmitting a beacon,when transmission and reception of data is not performed. In addition,even when the transmission and reception of data is not performed, it isalso obliged to perform a scan operation by operating a receiving devicecontinuously over one super frame once every several seconds (this timeinterval is defined as “T_SCAN” in this specification) and to confirmwhether there is any change in the presence of neighboring beacon orwhether there is a shift in the TBTT of each neighboring station.Further, when it is confirmed that there is a shift in the TBTT, theTBTT having a shift within −Bmin/2 ms is defined to be “advanced” andthe TBTT having a shift within +Bmin/2 ms is defined to be “delayed”based on the TBTT group recognized by the station, and the time isadjusted conforming to the most delayed TBTT.

NBOI Field

Further, FIG. 6 shows an example of description of a Neighboring BeaconOffset Information (NBOI) field as one piece of information transmittedby a beacon. In the NBOI, a position of a beacon which the relevantstation can receive (reception time) is written in a bit map by arelative position (relative time) from a position of a beacon thereof(transmission time). In the example shown in FIG. 6, although a casewhere the minimum interval is Bmin=5 [msec] and only sixteen kinds ofbeacon transmission positions can exist is referred to as an example andaccordingly an NBOI field length becomes 16 bits, the length is notnecessarily limited to 16 bits.

FIG. 6 shows an example of an NBOI field in which a communicationstation [No. 0] in FIG. 5 informs that “a beacon from a communicationstation [No. 1] and a communication station [No. 9] can be received”.With respect to a bit corresponding to a relative position of a beaconto which the reception is possible, a mark is assigned when a beacon isreceived and a space is assigned when a beacon is not received. The0.sup.th bit, the 1.sup.st bit, and 9.sup.th bit are marked in theexample of FIG. 6. The mark in the 0.sup.th bit shows that the beacon ofthe relevant station is transmitted, and the mark in the 1.sup.st bitshows that a beacon is received at timing delayed by Bmin*1 from theTBTT of this beacon. Similarly, the mark in the 9.sup.th bit shows thata beacon is received at timing delayed by Bmin*9 from the TBTT of thisbeacon.

Here, for a purpose other than the above, for example, such as a casewhere a supplementary beacon is transmitted, a mark may be assigned withrespect to a bit corresponding to timing at which a beacon is notreceived, though details are described later on.

NBAI Field

Further, a Neighboring Beacon Activity Information (NBAI) field similarto the NBOI field is defined here as information similarly transmittedby a beacon. In the NABI field, a position of a beacon which therelevant station actually receives (reception time) is written with abit map in a relative position from a position of a beacon thereof.Specifically, the NBAI field shows that the station is in an activestate capable of receiving. Furthermore, information that the stationreceives a beacon at the specified beacon position in the super frame isprovided by two information of the above-described NBOI and NBAI. Thatis, each communication station is informed of the following 2-bitinformation by the NBOI and NBAI fields included in the beacon.TABLE-US-00001 NBAI NBOI DESCRIPTION 0 0 Existence of a beacon is notrecognized at the time. 0 1 Existence of a beacon is recognized at thetime. 1 0 Being in an active state at the time. 1 1 Reception of beaconis being performed at the time.

Processing for Taking OR of NBOI/NBAI

FIG. 7 shows a view until a newly entered communication station A setsTBTT thereof based on NBOI of each beacon obtained from a beacon whichis received from a neighboring station by a scan operation.

It is assumed that the communication station is able to receive beaconsfrom three stations 0 through 2 within a super frame by the scanoperation.

The beacon reception time of a neighboring station is treated as arelative position to a normal beacon of the scanning station, and isdescribed in an NBOI field with a bit map form (as described above).Then, in the communication station A, NBOI fields of the three beaconshaving received from the neighboring stations are shifted in accordancewith the reception time of each beacon, and after correspondingpositions of bits are aligned on a time axis, the NBOI are integratedfor reference by taking OR of NBOI bits of each timing. Explainingspecifically a procedure thereof, the beacon 1 is received in a delay ofthree slots on the basis of transmission timing of the beacon 0. Thecommunication station retains this information in a memory or the like.Further, after three slots in the back of the NBOI field included in thebeacon 1 are shifted to the front, this information is retained in thememory or the like (second tier in FIG. 7). Similar processing is alsoperformed on the beacon 2 (third tier in FIG. 7).

A sequence obtained as a result of reference after the integration ofthe NBOI fields of neighboring stations is “1101, 0001, 0100, 1000”shown by “OR of NBOIs” in FIG. 7. The mark 1 indicates a relativeposition of the timing at which the TBTT is already set in the superframe, and the space 0 indicates a relative position of the timing atwhich the TBTT is not set. In this sequence, a place where the space (0)becomes the longest run length is a possible position for newlydisposing a beacon. In the example shown in FIG. 7, the longest runlength is three, and there can exist two possible positions. Then, thecommunication station A decides the 15.sup.th bit among them as the TBTTof the normal beacon thereof.

The communication station A starts transmission of a beacon aftersetting the time of the 15.sup.th bit as the TBTT of the normal beaconthereof (namely, the head of the super frame thereof). At this time, theNBOI field transmitted by the communication station A becomes as shownby “NBOI for TX (1 Beacon TX)” in FIG. 7, in which each reception timeof the beacon of the communication stations 0 through 2 whose beacon canbe received by the station A is written in the bit map form marking thebit position corresponding to the relative position from thetransmission time of the normal beacon thereof.

Further, when the communication station A transmits an auxiliary beaconfor a purpose of obtaining a priority transmission right and the like,the longest run length of the space (0) in the sequence shown by “OR ofNBOIs” which integrates the NBOI fields of the neighboring stations isfurther searched and the transmission time of the auxiliary beacon isset at a position of the space found. A case where two auxiliary beaconsare transmitted is assumed in the example shown in FIG. 7, andtransmission timing of the auxiliary beacon is set at the time of spaceof the 6.sup.th bit and at the time of space of the 11.sup.th bit in “ORof NBOIs”. In this case, the NBOI field transmitted by the communicationstation A is also marked in a place where the station transmits theauxiliary beacon (relative position to the normal beacon) in addition tothe normal beacon thereof and the relative position of the beaconreceived from the neighboring station, and this NBOI field becomes asshown by “NBOI for TX (3 Beacon TX)”.

In the case where each communication station performs transmission of abeacon by setting the beacon transmission timing TBTT thereof in such aprocessing procedure as the one described above, a collision of beaconscan be avoided under a condition that each communication station standsstill so that a reaching range of an electric wave does not fluctuate.In addition, since an auxiliary beacon (or a signal similar to aplurality of beacons) is transmitted within a super frame according tothe priority of transmission data, resources can be preferentiallyallocated to provide QoS communication. Further, since eachcommunication station can autonomously obtain a saturation level of asystem by referring to the number of beacons (NBOI fields) received fromneighbors, it becomes possible to accommodate priority traffic inconsideration of the saturation level of the system for eachcommunication station despite of a distributed control system. Further,since each communication station refers to a NBOI field of a receivedbeacon and the beacon transmission time is disposed not to collide witheach other, it is possible to avoid such a situation that a collisionoccurs frequently even when a plurality of communication stationsaccommodate priority traffic.

Thus, when a communication station newly enters a network, the center ofa period where a run length of the space becomes the longest isdetermined as beacon transmission timing based on a result of a sum ofNBOI obtained from a beacon received from each communication station.

The example of referring to the NOBI fields by the OR is shown in theexplanation above, further in case of an NBAI field, control isperformed not to transmit at the beacon transmission time of markedtiming by a similar procedure of referring to a sum (OR).

Specifically, when a communication station transmits some information, abeacon transmitted from a neighboring communication station is receivedas needed, and control is performed not to transmit at the beacontransmit time of marked timing based on a result of a sum (OR) of anNBAI field obtained from a beacon received from each communicationstation.

FIG. 8 shows processing at this time. Here, a case where an NBAI fieldhas eight bits is shown as an example, in which the 0.sup.th bit, the4.sup.th bit and the 6.sup.th bit are marked as a result of a sum (OR)of respective NBAI fields of reception beacons obtained in accordancewith the above-described procedure. The 0.sup.th bit is a beaconthereof, and additional processing is not specifically performed. Sincethe 4.sup.th bit is marked, a transmission permission flag thereof islowered so as not to perform transmission at the time T4 that is thebeacon transmission time of the 4.sup.th bit. Further, similarly withrespect to the 6.sup.th bit the transmission permission flag thereof islowered so as not to perform transmission at the corresponding time T6.Accordingly, when a certain communication station wishes to receive abeacon of another communication station, there is no such case that atransmission station interrupts the reception thereof and highlyreliable transmission and reception can be performed.

Transmission Prioritized Period TPP

Each communication station transmits a beacon at a fixed interval, andin this embodiment after a beacon is transmitted, the priority oftransmission for a while is given to a station having transmitted thebeacon. FIG. 9 shows a view in which the priority of transmission isgiven to a beacon transmission station. FIG. 9 shows as an example acase where 480 [.mu.sec] is given as the transmission prioritizedperiod. This prioritized period is defined as a Transmission PrioritizedPeriod (TPP). The TPP starts immediately after beacon transmission andends at the time after a lapse of T_TPP from TBTT. Since eachcommunication station transmits a beacon in each super frame, the TPP ofthe same time rate is basically distributed to each communicationstation. After a TPP of one communication station ends, a period untilanother communication station transmits a beacon becomes a Fairy AccessPeriod (FAP). In the Fairy Access Period (FAP), a fair mediumacquisition competition is performed by an ordinary CSMA/CA method (or,a PSMA/CA method described later on).

FIG. 10 shows a structure of a super frame. As shown in this figure,subsequently to transmission of a beacon from each communicationstation, a TPP is allocated to the communication station havingtransmitted the beacon, a FAP is started after time lapses by a lengthof the TPP, and the FAP ends when a beacon is transmitted from a nextcommunication station. It should be noted that an example in which theTPP starts immediately after the transmission of the beacon is shownherein, however not limited to this example, the start time of the TPPmay be set at a relative position (time) from the transmission time of abeacon, for example. In addition, there is also a case in which the TPPis defined as 480 [.mu.sec] from the TBTT. In addition, as shown in FIG.9, since a range of the TPP ends after the period of T_TPP from the TBTTas a basis, the range of the TPP is deleted when the transmission timeof a beacon delays due to TBTT offset.

An example of a typical transmission and reception procedure of acommunication station is explained using FIGS. 11A to 11C. In FIGS. 11Ato 11C, an explanation with respect to the communication station STA0and the communication station STA1 is made by referring a case, in whichtransmission is performed from the communication station STA0 to thecommunication station STA1, as an example. Each communication stationdoes not necessarily receive a beacon signal of another station eachtime. There is also a case where a frequency of reception is lowered byinstructions and the like from an upper layer. FIG. 11A shows a sequencechart of a packet transmitted and received between the communicationstations STA0 and STA1; FIG. 11B shows a state of the transmission unitof the communication station STA0; and FIG. 11C shows a state of thereception unit of the communication station STA0. With respect to thestate of the transmission and reception units, a high level shows anactive state (a state of trying transmission or reception) and a lowlevel shows a sleep state.

First, the communication station STA0 transmits a beacon afterconfirming that a medium is clear. It is assumed that the communicationstation STA1 is called up in TIM and (or) PAGE in this beacon. Thecommunication station STA1 having received this beacon makes a responseto the paging information (0). Since this response corresponds to themiddle of the TPP of the communication station STA0 and the priorityright has been obtained, the transmission is performed at a SIFSinterval. After that, since the transmission and reception during theTPP between the communication station STA1 and the communication stationSTA0 has the priority right, transmission is performed at the SIFSinterval. After confirming that the communication station STA1 is in astate capable of receiving, the communication station STA0 havingreceived the response transmits a packet addressed to the communicationstation STA1 (1). Further, since there exists another packet addressedto the communication station STA1 in FIG. 11A, one more packet istransmitted (2). The communication station STA1 having received twopackets transmits an ACK after confirming that those packets arereceived properly (3). After that, the communication station STA0transmits the last packet (4). However, while receiving the previousACK, the TPP of the communication station STA0 is ended and the FAP isalready started at the time of transmission of (4). Since there is nopriority right of transmission in the FAP, the transmission is performedat an interval of LIFS+ back-off with respect to the packet (4). An ACKcorresponding to the packet (4) is transmitted by the communicationstation STA1 (5).

A certain period of time after the last transmission is performed isdefined as a Listen Window, and each communication station is obliged tooperate a receiving device. FIG. 11 also shows the aspect thereof. Whenthere exists no reception packet during a listen period, thecommunication station changes a state to a sleep state and stops atransmission and reception device to try to reduce power consumption.Details of power saving operation of each terminal is explained in thefollowings.

Definition of Activity Level

Power saving is automatically practiced at the time when transmissionand reception of data is not performed, and at the time whentransmission and reception of data is performed, a correspondingprocessing procedure is operated. An intermittent operation rate of anMAC layer fluctuates according to the presence or absence oftransmission and reception data.

FIG. 13 is a diagram showing a definition and a transition of anactivity level which is set to each communication terminal in thisembodiment. Hereupon, four stages from an active level 0 to an activelevel 3 are defined based on an operation rate and the like. Although adetailed transmission and reception procedure of each activity level isdescribed later on, brief explanation is made here with respect to eachactivity level.

The active level 0 corresponds to a state in which information and asignal are not transmitted and received with another station. Thisactive level 0 is a state in which a receiving device is only operatedat the time of transmission of a beacon and around beacon transmissiontiming. When data to be transmitted is generated from an upper layer orwhen being called up from another station under this state, a transitionis made to the active level 1.

The active level 1 corresponds to a state in which transmission andreception is performed with a specific station (or, all communicationstations existing in the neighborhood) in a minimum level of band. Thisactive level 1 is a state in which transmission and reception processingis performed mutually regarding to transmission and reception of abeacon, and the transmission and reception of data and the like isperformed as a result thereof. When it is judged that the volume of datato be transmitted and received becomes too much to handle by the activelevel 1, a transition is made to the active level 2.

The active level 2 is a state in which a transmission trigger isgenerated dispersively in between the transmission time of a beacontransmitted in each super frame, and transmission and reception of datais performed even at a point of time that the transmission trigger isactivated. When it is judged that the volume of data to be transmittedand received becomes too much to handle by the active level 2, atransition is made to the active level 3.

The active level 3 corresponds to a state in which transmission andreception of data is performed in all period of times. A transmissionstation and a reception station perform continuously a transmission andreception operation, and a transmission procedure is started immediatelywhen data to be transmitted is generated on the transmission side.

When it is judged that time during which the volume of data to betransmitted is judged small becomes sufficiently long (that is managedusing a timer, for example) in each activity level, a transition is madeto an activity level of one level below.

Neighboring Station List (Neighbor List)

FIG. 12 is a diagram showing a part of a neighbor list in thisembodiment.

Each communication station retains neighboring station information byeach station, and this information is managed in a form called theneighbor list. In the neighbor list, transmission timing of a beacon, astate of propagation path with the relevant station, and the like arestored with respect to each station.

In this embodiment, the activity level of each neighboring station isseparately obtained and managed with respect to transmission andreception in this neighbor list. In FIG. 12, examples of neighbor listsof the communication station STA0 (left side of FIG. 12) and thecommunication station STA1 (right side of FIG. 12) in FIG. 4 is shown.In the neighbor list of the communication station STA0, data on threestations of communication stations STA1, STA2 and STA3 from which thecommunication station STA0 can receive a beacon is registered as arecord, in which the activity level referred to at the time oftransmission and the activity level referred to at the time of receptionare written with respect to each station. In the example shown here, acase where both the communication stations STA0 and STA1 are in theactivity level 0 (shown as ACT-0 in the figure) in both transmission andreception with respect to all stations is described.

Operation at the Time of Active Level 0

FIGS. 14A to 14D are diagrams showing a transmission and receptionprocedure in the case of the active level 0. In this figure, anexplanation is made with respect to the communication station STA0 andthe communication station STA1. FIG. 14A is a state of receptionoperation in the communication station STA0, FIG. 14B is a state oftransmission in the communication station STA0, FIG. 14C is a state oftransmission in the communication station STA1, and FIG. 14D is a stateof reception operation in the communication station STA1. With respectto the state of reception operation, a high level shows the receptionoperation, and a low level shows suspension of reception operation(those are similar regarding a state of reception operation in thefigures on and after FIG. 15). Hereinafter, an explanation is made usingsimilar figures.

In the active level 0, each communication station operates a receptionunit prior to the beacon transmission time thereof in order to judgewhether a medium is clear; transmits a beacon at the beacon transmissiontime when the medium is clear; subsequently operates the reception unitover a period of time called the above-described listen window; andstops transmission and reception units until the next beacontransmission if data addressed thereto is not received. Specifically,the active level 0 is a state to perform a minimum necessary level oftransmission and reception processing, and is a mode to perform a lowestpower consumption operation. The following operations are performed inthe active level 0.

Beacon transmission operation in each super frame cycle (T_SF)

Reception operation during a listen window after the beacon transmission

Scan operation performed over a super frame cycle (T_SF) at each T_SCAN

In the active level 0, Latency required for data transmission andreception becomes the super frame cycle T_SF [msec] at maximum on oneway. Since a beacon of another station is not received in this operationmode, a low power consumption operation in hardware is obtained.

A reception activity level relating to the communication station STA1 inthe neighbor list of the communication station STA0 is shown in theuppermost tier of FIG. 14 (upper side of FIG. 14A), and this correspondsto item (A)(2) in the neighbor list of the communication station STA0 inFIG. 12. A transmission activity level relating to the communicationstation STA1 in the neighbor list of the communication station STA0 isshown directly under the reception activity level, and this correspondsto item (A)(1) in the neighbor list of the communication station STA0 inFIG. 12.

Further, a reception activity level relating to the communicationstation STA0 in the neighbor list of the communication station STA1 isshown directly under the reception state of FIG. 14D, and thiscorresponds to item (A)(2) in the neighbor list of the communicationstation STA1 in FIG. 12. A transmission activity level relating to thecommunication station STA0 in the neighbor list of the communicationstation STA1 is shown in the lowest tier of FIGS. 14A to 14D, thiscorresponds to item (A)(1) in the neighbor list of the communicationstation STA1 in FIG. 12. Hereinafter, an explanation is made also on theassumption that a similar relation of correspondence exists.Specifically, the content of the neighbor list in FIG. 12 also describesthe activity level of each terminal shown in FIG. 14.

In the case where there exists data to be transmitted or to be receivedduring a process of transmission and reception processing in theabove-described active level 0, a transition is made to the active level1.

Operation at the Time of Active Level 1

FIGS. 15A to 15D are diagrams showing a transmission and receptionprocedure in a case of the active level 1. The active level 1 is a statein which a beacon of a neighboring station is received in addition tothe operation of the active level 0, and power consumption fluctuatesaccording to the number of neighboring stations. In the active level 1,activities described below are performed.

Beacon transmission operation in each super frame cycle (T_SF)

Reception processing operation during a listen window after beacontransmission

Reception processing operation of beacons from neighboring stationsrecognized by the relevant station

Scan operation performed over super frame cycle (T_SF) at each T_SCAN

FIG. 15A is a state of reception operation in the communication stationSTA0, FIG. 15B is a state of transmission and reception of a packet inthe communication station STA0, FIG. 15C is a state of transmission andreception of a packet in the communication station STA1, and FIG. 15D isa state of reception operation in the communication station STA1.Further, a reception (Rx) activity level and a transmission (Tx)activity level in the communication station STA0 are shown on the upperside of FIG. 15A, and a reception (Rx) activity level and a transmission(Tx) activity level in the communication station STA1 are shown on thelower side of FIG. 15D. In FIGS. 15A to 15D, a case where a transitionfrom the active level 0 to the active level 1 is made in accordance witha transmission request from the communication station STA0 and afterthat the state returns to the active level 0 is referred to as anexample.

Initially, the activity level of transmission and reception is 0 in boththe communication stations STA0 and STA1; when data D0 to be transmittedto the communication station STA1 is generated in the communicationstation STA0, a reception activity level of the communication stationSTA0 with respect to the communication station STA1 makes the transitionto the level 1 at that time and a beacon of the communication stationSTA1 is received at the beacon (B1-3) transmission time of thecommunication station STA1. When paging information that there is atransmission request to the communication station STA1 is transmitted bymaking this beacon reception a trigger, the communication station STA1recognizes that “the STA0 has information to be transmitted to theaddress thereof”, and the activity level of both the transmission andreception relating to the communication station STA0 is changed to thelevel 1. Further, the communication station STA1 returns an ACKindicating that the above-described paging information is acknowledgedto the communication station STA0, and the communication station STA0having received this ACK changes the transmission activity levelrelating to the communication station STA1 to the level 1.

After that, at the beacon transmission time of the communication stationSTA0, the communication station STA0 calls up the communication stationSTA1 by a beacon (B0-4) after confirming that the transmission activitylevel relating to the communication station STA1 is the level 1 in theneighbor list. Since the reception activity level relating to thecommunication station STA0 is the level 1, the communication stationSTA1 receives this beacon and returns an ACK responding to this call.This call and response assumes a roll corresponding to a RTS and CTS ina RTS/CTS procedure, and after that the data D0 is transmitted in orderto transmit from the communication station STA0 to the communicationstation STA1. Then, the communication station STA1 returns an ACK.Although both the communication stations STA0 and STA1 operate thereception units over the listen window (LW) after that, the receptionunits are stopped afterwards due to a reason that there exists noreception data.

In the active level 1, basically with beacon transmission on the datatransmission side as the start, transmission and reception of data isperformed according to the above-described procedure. Here, whentransmission data is small, the communication station STA0 can alsotransmit the data immediately after the beacon (B1-3) transmitted by thecommunication station STA1.

Further, hereupon the example in which there exist two stations of STA0and STA1 is explained, however, in the case where further more stationsexist in the neighborhood, there is also a case that a station in whicha transmission activity level with respect to any one of stationsbecomes the level 1 (that is, a station which transmits data to any oneof stations) performs beacon reception of a station in whichtransmission and reception activity levels are set to the level 0.

In the example of FIG. 15, a process of making the transition to theactive level 0 after that is shown. After the previous data D0 istransmitted and received, the communication station STA1 transmits abeacon (B1-5) at the beacon transmission timing thereof. Though thecommunication station STA0 receives this beacon, nothing happens.Further after that, the communication station STA0 transmits a beacon(B0-6) at the beacon transmission timing thereof. Although thecommunication station STA1 receives this beacon, nothing is transmittedthereto. Then, the communication station STA1 decides to change theactivity level relating to the communication station STA0 to the level0. After that, the communication station STA1 notifies that “the STA1changes the reception activity level relating to the STA0 to the level0” in a beacon (B1-7) to be transmitted at the beacon transmissiontiming thereof or data (not shown in the figure) to be transmittedimmediately thereafter, and the activity level is changed to the level 0as notified. The communication station STA0 having received this noticechanges the transmission activity level relating to the communicationstation STA1 to the level 0. Further after that, the communicationstation STA0 notifies that “the STA0 changes the reception activitylevel relating to the STA1 to the level 0” in a beacon (B0-8) to betransmitted at the beacon transmission timing thereof, and changes theactivity level to the level 0.

Although the communication station STA1 has changed the activity levelto the level 0 on the ground that data is not transmitted following thebeacon (B0-6) in the above-described example, there is also a case wherethe activity level is changed on the ground that data is not transmittedthough a plurality of beacons are received successively.

Further, it is also possible to have a timer monitoring time when notransmission and reception of traffic is performed and the activitylevel is lowered by making the expiration of the timer as a trigger. Atthis time, it is necessary to set separately a timer to lower a Tx.Active Level and a timer to lower a Rx. Active Level, and a margin isgiven by setting the time set to the timer of lowering the Tx. ActiveLevel shorter than the timer of lowering the Rx. Active Level and it ispossible to prevent from being generated such useless traffic that “areceiving device has not received data though transmitted”.

In addition, although the procedure of notifying that the activity levelis lowered is performed in the above-described example, there is also acase where this procedure is omitted. In this case, processing isperformed such that the STA1 on the reception side automatically changesthe activity level when data is not received from the STA0 over N beaconcycles, and the STA0 on the transmission side automatically changes theactivity level when an ACK (acknowledgement) of data is not receivedfrom the STA1 over an N-1 beacon cycles. Useless processing can beomitted by making the beacon cycle on the transmission side set short.

Other than the above, there is also a case where the activity level ischanged to the level 0 on the ground that “transmission and reception ofdata is only performed dispersively exceeding a permissible value”.

Further, although the communication station STA1 that is the receptionside decides that “the activity level is changed from the level 1 to thelevel 0” in the example described above, there is also a case where thecommunication station STA0 that is the transmission side makes such adecision and the reception side follows the decision. Since a procedurein this case is similar to the procedure explained above, an explanationthereof is not specifically made here.

In the active level 1, Latency required for data transmission andreception is the super frame cycle T_SF [msec] at maximum on one way.The active level 1 is assumed to be such a state that signaling isoccasionally exchanged but traffic does not actually performed.

When it is recognized that data to be transmitted or to be receivedexists regularly during the process of transmission and receptionprocessing in the active level 1, a transition is made to the activelevel 2. A judgment whether the data to be transmitted or to be receivedexists regularly is made by monitoring if the number of packetsaccumulated in the transmission buffer exceeds a predetermined thresholdvalue, for example.

Transition from Active Level 1 to Active Level 2

The active level 2 is a state in which a transmission and receptiondevice is operated periodically in addition to the operation of theactive level 1, and is a mode to perform the low power consumptionoperation by the intermittent transmission and reception though data istransmitted and received.

The following activities are performed in the active level 2.

Beacon transmission operation in each super frame cycle T_SF

Reception processing operation during a listen window after beacontransmission

Reception processing operation of beacons of neighboring stationsrecognized by the relevant station

Reception processing operation (transmission processing operation isalso performed according to necessity) at the time specified (or to bespecified)

Scan operation performed over a super frame cycle T_SF at each T_SCAN

FIGS. 16A to 16D are diagrams showing a transition from the active level1 to the active level 2. FIG. 16A is a state of reception operation inthe communication station STA0, FIG. 16B is a state of transmission andreception of a packet in the communication station STA0, FIG. 16C is astate of transmission and reception of a packet in the communicationstation STA1, and FIG. 16D is a state of reception operation in thecommunication station STA1. Further, a reception (Rx) activity level anda transmission (Tx) activity level in the communication station STA0 areshown on the upper side of FIG. 16A, and a reception (Rx) activity leveland a transmission (Tx) activity level in the communication station STA1is shown on the lower side of FIG. 16D. In FIG. 16, a case where thetransition is made in accordance with a transmission request from thecommunication station STA0 is referred to as an example.

In an initial state of FIG. 16, the transmission and reception of datais performed in a state where both the communication stations STA0 andSTA1 are in the level 1 with respect to the transmission and receptionlevels relating to each other, and the transmission data D0 to thecommunication station STA1 which has reached the communication stationSTA0 is transmitted with transmission of a beacon (B0-10) of thecommunication station STA0 as the start. After that, transmission dataD1 and D2 to the communication station STA1 reach the communicationstation STA0 before again the time becomes the beacon transmissiontiming of the communication station STA0. At this time, thecommunication station STA0 judges that the transmission data addressedto the communication station STA1 is accumulated in excess of apermissible value, and decides to change the transmission activity levelto the level 2.

When a beacon (B0-12) is transmitted at the beacon transmission timingof the communication station STA0, the communication station STA0notifies that the STA0 wishes to change the activity level to the level2 while calling up the communication station STA1 by the beacon. Thecommunication station STA1 having received this notice changes thereception activity level relating to the communication station STA0 tothe level 2 as notified, and returns an ACK of acknowledgement. Thecommunication station STA0 having received this acknowledgement confirmsthat the reception activity level of the communication station STA1 ischanged to the level 2, and changes the transmission activity level tothe level 2. Further, although both the communication station STA0 andthe communication station STA1 operate the reception units only duringthe listen window (LW) after the transmission data D1 and D2 previouslyaccumulated are transmitted with the beacon (B0-12) as the start and aresponse thereof is obtained, the reception units are stopped since datais not received any further. After that, since the communication stationSTA0 is in the state of the transmission activity level 2, thetransmission and reception device is operated at the time specified bythe transmission active level 2 of the communication station STA0, andtransmission of data D3 accumulated during this period is tried afterexecuting a predetermined procedure. On the other hand, thecommunication station STA1 is in a state synchronized with the activelevel 2 of the communication station STA0, operates the receiving devicesimilarly at the time specified by the transmission active level 2 ofthe communication station STA0, receives the transmitted data D3, andreturns an ACK.

Further, the communication station STA0 that is the transmission sidedecides to make the transition of the activity level to the level 2 dueto a reason that “it is judged that the transmission data addressed tothe communication station STA1 has accumulated in excess of thepermissible value” in the above-described example, however other thanthis, there are a case caused by a reason that “supposing thattransmission of data is started immediately after the beacontransmission thereof, it is judged that the transmission of data may notbe completed within a certain period of time”, a case caused by a reasonthat “a response from a reception station is not received to the callingmade within a category of the active level 1”, and the like.

Operation at the Time of Active Level 2

FIGS. 17A to 17E are diagrams showing a transmission and receptionprocedure in a case of the active level 2. FIG. 17A is a state ofreception operation in the communication station STA0, FIG. 17B shows astate in which a transmission trigger signal is generated in thecommunication station STA0, FIG. 17C is a state of transmission andreception of a packet in the communication station STA0, FIG. 17D is astate of transmission and reception of a packet in the communicationstation STA1, and FIG. 17E is a state of reception operation in thecommunication station STA1. Further, a reception (Rx) activity level anda transmission (Tx) activity level in the communication station STA0 areshown in the upper side of FIG. 17A, and a reception (Rx) activity leveland a transmission (Tx) activity level in the communication station STA1are shown in the lower side of FIG. 17E. In FIGS. 17A to 17E, a casewhere data is transmitted from the communication station STA0 to thecommunication station STA1 is shown as an example, referring to a casewhere a transmission trigger generated between beacons is generatedtwice.

In the active level 2, the transmission trigger is generated at the timedefined by the relative time from beacon transmission timing on thetransmission side, and transmission of data is performed with thegeneration of this transmission trigger as the start in addition to thetransmission of a beacon. First, an explanation is made to the procedureof data transmission and reception which is performed at the time of theactive level 2, and it is described later on when the transmissiontrigger is generated.

In an initial state of FIG. 17, it is assumed that the activity levelsof both transmission and reception sides have already become the level2. The communication station STA0 that is a transmission stationtransmits D4 and D5 which are transmission data accumulated until then,by making transmission of a beacon (B0-14) a trigger. Since there is nomore accumulated transmission data at a point of time when thetransmission of D5 is completed, the transmission is once suspended andthe reception units are stopped after both the communication stationsATA0 and STA1 make the reception units operated for the period of thelisten window (LW). Hereupon, when new transmission data is providedduring the period of this listen window (LW), the data is immediatelytransmitted, though not shown in the figure.

After that, although transmission data D6 is newly supplied to thecommunication station STA0, the communication station STA0 retains thedata since the transmission and reception has been suspended. Duringthis period, both the communication station STA0 and the communicationstation STA1 monitor an elapsed time from the transmission time of theprevious beacon (B0-14) of the communication station STA0 using timersprovided therein, and a transmission trigger is generated after apredetermined time T-AL2(1) [.mu.sec] elapses. The communication stationSTA0 tries to transmit accumulated data addressed to the communicationstation STA1 with the generation of this transmission trigger as thestart. On the other hand, similarly the communication station STA1 alsooperates the receiving device when the time T-ALT2(1) [.mu.sec] elapsesfrom the transmission time of the previous beacon (B0-14) to be readyfor transmission from the communication station STA0.

Accordingly, data D6 and D7 which are accumulated in the communicationstation STA0 are transmitted and received with this transmission triggeras the start. After the transmission and reception of the data D7 iscompleted, the communication station STA0 and the communication stationSTA1 suspend the transmission, because there is no more accumulatedtransmission data, and both the communication stations STA0 and STA1stop the reception units after the reception units are operated duringthe period of the listen window (LW). After that, although new data D8is supplied to the communication station STA0, the communication stationSTA0 retains this data, because the transmission and reception has beensuspended. Even during this period, both the communication station STA0and STA1 monitor an elapsed time from the transmission time of theprevious beacon (B0-14) of the communication station STA0 using thetimers provided therein, and a new transmission trigger is generatedwhen a predetermined time T-AL2(2) [.mu.sec] elapses from the previouslygenerated transmission trigger. The communication station STA0 and thecommunication station STA1 again perform transmission and reception ofdata according to the above-described procedure with the generation ofthis transmission trigger as the start.

Then, similar processing is repeated until a next transmission beacon(B0-16) of the communication station STA0 is generated.

Example of Setting T-AL2(i) at Active Level 2

A purpose to define the active level 2 is to reduce power consumption bysupplementing the T_SF that is the beacon interval and by using theintermittent operation at the same time while providing shorter latencybut allowing some latency. Further, it is desirable that the time ofgenerating this transmission trigger does not mutually overlap withother communication stations in order to avoid a collision with atransmission packet of another station and to improve the performance atthe MAC level.

Particularly, when the number of communication stations accommodated ina network is small, a transmission station generates in the active level2 a transmission trigger such that a transmission operation can bestarted at each T-AL2(i), based on the reference time that determinesthe beacon transmission time thereof or based on the beacon transmissiontime such as the TBTT, in consideration of satisfying theabove-described matters as much as possible. The T-AL2(i) (i=1, 2, - - -) is obtained by the following formula.T.sub.-AL2.sub.-i=(N AL2 STEP+AL2TBL[i])*T Bmin+N AL2 TRX STT OFFSET+N AL2 TRX STT OFFSET STEP*i, whereinAL2 TBL[i]=[0, −1, 0, 0, 0, 1]

For example, when the above-described operation is performed at T_SF=40msec, T Bmin=625 [.mu.sec], N AL2 STEP=9, N AL2 TRX STT OFFSET=180[.mu.sec], and N AL2 TRX STT OFFSET STEP=10.0 [.mu.sec], eachtransmission trigger time T AL 2[i] is set to:T AL2[0]=TBTTT AL2[1]=TBTT+5.625[msec]+190[.mu.sec]T AL2[2]=TBTT+10.625[msec]+200[.mu.sec]T AL2[3]=TBTT+16.250[msec]+210[.mu.sec]T AL2[4]=TBTT+21.875[msec]+220[.mu.sec]T AL2[5]=TBTT+27.500[msec]+230[.mu.sec]T AL2[6]=TBTT+33.750[msec]+240[.mu.sec]and the time at which transmission is possible appears at intervals ofapproximately 6.25[msec].

For example, when bulk transfer of an FTP and the like is performedthrough a TCP of MAX WIN SIZE=64 kByte, latency of both ways becomes12.5 [msec] at the worst value, and a limit of throughput resulted fromflow control of the TCP becomes 40.96 [Mbps]. If a processing delayrequired for transmission and reception is estimated at 1.0 [msec], itis possible to provide up to 35.31 [Mbps].

Further, when the setting is the above-described T AL2[*], and in casethat the TBTT exists at every T Bmin from 0 to 63, a macroscopiccollision of T AL2[*] becomes as follows, when those that collide with acommunication station of TBTT=0 are picked up.TBTT=8, 56.times.one timeTBTT=20, 28, 36, 44.times.one timeTBTT=10, 18, 26, 38, 46, 54.times.two timesTBTT=17, 19, 27, 29, 35, 37, 45, 47.times.two timesTBTT=9, 55.times.four times

The collision of the T AL2[*] does not occur when the number ofcommunication stations is 4 or less, the collision with two stationsoccurs one time each when the number of communication stations is eightor less, and the possibility of collision may increase as the number ofcommunication stations increases more than that. Although a receptionstation is in a state in which reception and transmission can beperformed at a designated T AL2[i], the reception station makes atransition to an idle state again after a receiving device is operatedduring a period of T LW when no data is transmitted thereto. Inaddition, when a reception node recognizes that information addressed tothe relevant reception node is not transmitted at the designated TAL2[i], a time rate of an active state may be lowered after notifying acommunication station of transmission source that reception operation isperformed only at the time of any of T AL2(i).

Further, although six sets of transmission trigger time are defined asthe active level 2 in the above-described example, the present inventionis not limited thereto.

Furthermore, such processing, in which a plurality of stages are definedin the active level 2, three sets of transmission trigger time aregenerated at an active level 2-1, and six sets of transmission triggertime are generated at an active level 2-2, is also within a rangeconceivable from the present invention.

Transition from Active Level 2 to Active Level 1

FIGS. 18A to 18E are diagrams showing a transition from the active level2 to the active level 1. FIG. 18A is a state of reception operation inthe communication station STA0, FIG. 18B shows a state in which atransmission trigger signal is generated in the communication stationSTA0, FIG. 18C is a state of transmission and reception of a packet inthe communication station STA0, FIG. 18D is a state of transmission andreception of a packet in the communication station STA1, and FIG. 18E isa state of reception operation in the communication station STA1.Further, a reception (Rx) activity level and a transmission (Tx)activity level in the communication station STA0 are shown on the upperside of FIG. 18A, and a reception (Rx) activity level and a transmission(Tx) activity level in the communication station STA1 are shown on thelower side of FIG. 18E. In FIGS. 18A to 18E, a case where the transitionis made in accordance with a request from the communication station STA1is referred to as an example.

In an initial state in FIGS. 18A to 18E, the transmission and receptionof data is performed in a state where both the communication stationsSTA0 and STA1 are in the level 2 with respect to the transmission andreception levels relating to each other, and the transmission andreception of data is performed from the communication station STA0 tothe communication station STA1 with transmission of a beacon of thecommunication station STA0 or transmission of the generation of atransmission trigger as the start.

In this figure, first the communication station STA0 transmits a beacon(B0-16), and transmission data D10 and D11 which have been accumulatedin the communication station STA0 are transmitted and received with thisbeacon transmission as the start. After that, the reception unit isoperated over the period of the listen window (LW), and then thetransmission and reception is suspended. After that, the T-AL2(1)[.mu.sec] elapses from the transmission time of the previous beacon(B0-16), and a transmission trigger is generated. Although both thecommunication stations STA0 and STA1 operate the reception units aroundthis time, no transmission and reception is performed since there is notransmission data accumulated in the communication station STA0, and thereception units are again stopped after the period of the listen window(LW) elapses from the generation of the transmission trigger. Further,the T-AL2(2) [.mu.sec] elapses from the generation of this transmissiontrigger, a transmission trigger is again generated, the communicationstations STA0 and STA1 perform similar operations, but there is no datatransmitted and received.

Further after that, although the communication station STA0 transmits abeacon (B0-18), there is also no data transmitted and received. At thispoint of time, the communication station STA1 decides that the receptionactivity level relating to the communication station STA0 is changed tothe level 1 on the ground that transmission data does not exist over onebeacon transmission cycle. After that, the communication station STA1notifies that “the STA1 changes the transmission and reception activitylevel relating to the STA0 to the level 1” in a beacon (B1-19) to betransmitted at the beacon transmission timing thereof or in data (notshown in the figure) to be transmitted immediately after that, andchanges the activity level to the level 1 as notified. The communicationstation STA0 having received this notice changes the transmissionactivity level relating to the communication station STA1 to the level1.

Although the communication station STA1 changes the activity level tothe level 1 on the ground that “data does not exist over one beacontransmission cycle” in the above-described example, there is also a casewhere the activity level is changed on the ground that “data does notexist over a plurality of cycles”.

Further, although the procedure of notifying that the activity level islowered is performed in the above-described example, there is also acase where this procedure is omitted. In this case, processing isperformed such that the STA1 on the reception side automatically changesthe activity level when data is not received from the STA0 over N beaconcycles, and the STA0 on the transmission side automatically changes theactivity level when an ACK (acknowledgement) of data is not receivedfrom the STA1 over N-1 beacon cycles. Useless processing can be omittedby making the beacon cycle on the transmission side set short.

In addition, although the communication station STA1 that is thereception side decides that “the activity level is changed from thelevel 2 to the level 1” in the above-described example, there is also acase where the communication station STA0 that is the transmission sidemakes such a decision and the reception side follows this decision.Since a procedure in this case is similar to the procedure explainedabove, an explanation thereof is not specifically made here.

Transition from Active Level 2 to Active Level 3

The active level 3 is a state in which a reception operation isperformed regularly even during an idle period of time in addition tothe operation of the active level 1, and a operation of detecting acarrier (or preamble) transmitted by another communication station isconsecutively performed. This active level 3 is a mode which provides aswide a band as possible and as short the latency as possible by thisactive level, though the efficiency of reducing power consumption issmall.

The following operations are performed in the active level 3.

Beacon transmission operation in each super frame cycle T_SF

Reception processing operation during a listen window after the beacontransmission

Continuous reception processing operation

FIGS. 19A to 19E are diagrams showing a transition from the active level2 to the active level 3. FIG. 19A is a state of reception operation inthe communication station STA0, FIG. 19B shows a state in which atransmission trigger signal is generated in the communication stationSTA0, FIG. 19C is a state of transmission and reception of a packet inthe communication station STA0, FIG. 19D is a state of transmission andreception of a packet in the communication station STA1, and FIG. 19E isa state of reception operation in the communication station STA1.Further, a reception (Rx) activity level and a transmission (Tx)activity level in the communication station STA0 is shown on the upperside of FIG. 19A, and a reception (Rx) activity level and a transmission(Tx) activity level in the communication station STA1 is shown on thelower side of FIG. 19E. In FIGS. 19A to 19E, a case where the transitionis made in accordance with a transmission request from the communicationstation STA0 is referred to as an example.

In an initial state of FIGS. 19A to 19E, the transmission and receptionof data is performed in a state where both the communication stationsSTA0 and STA1 are in the level 2 with respect to the transmission andreception levels relating to each other, and the transmission data D8,D9 and D10 to the communication station STA1 which have been accumulatedin the communication station STA0 are transmitted with the generation ofa transmission trigger as the start. After that, although the receptionunit is operated over the listen window (LW), the transmission andreception is suspended, because new transmission data is not generated.However, transmission data D11 and D12 to the communication station STA1reach the communication station STA0 prior to the time of transmitting abeacon (B0-20) of the communication station STA0 that is a nexttransmission opportunity. At this time, the transmission station STA0judges that the transmission data addressed to the communication stationSTA1 have been accumulated in excess of a permissible value, and decidesto change the transmission activity level to the level 3.

When the beacon (B0-20) is transmitted at the beacon transmission timingof the communication station STA0, the communication station STA0notifies that the STA0 wishes to change the activity level to the level3 while calling up the communication station STA1 by the beacon. Thecommunication station STA1 having received this notice changes thereception activity level to the level 3 as notified, and returns an ACKof acknowledgement. The communication station STA0 having received thisACK confirms that the reception activity level of the communicationstation STA1 is changed to the level 3, and changes the transmissionactivity level relating to the communication station STA1 to the level3. Further, on and after the transmission data D11 which have beenaccumulated are transmitted sequentially with the transmission of thebeacon (B0-20) as the start, and the communication station STA1 receivesthe transmitted data sequentially.

In the active level 3, the transmission procedure is started immediatelywhen new transmission data arrives at the transmission side, anddelivery of the transmission data as early as possible is attempted. Onthe other hand, the reception side keeps the reception unit operating,and is prepared for reception of data addressed thereto though it isuncertain when the data is transmitted.

In the above-described example, the communication station STA0 that isthe transmission side decides to make the transition of the activitylevel to the level 2 due to the reason that “it is judged that thetransmission data addressed to the STA1 has accumulated in excess of thepermissible value”, however, other that this, there are also a casecaused by a reason that “supposing that the accumulated transmissiondata is transmitted with the transmission trigger as the start, it isjudged that the transmission of data may not be completed within acertain period of time”, a case caused by a reason that “a response isnot received to the calling of the reception station which is madewithin a category of the active level 2”, and the like.

Transition from Active Level 3 to Active Level 2

FIGS. 20A to 20E are diagrams showing a transition from the active level3 to the active level 2. FIG. 20A is a state of reception operation inthe communication station STA0, FIG. 20B shows a state in which atransmission trigger signal is generated in the communication stationSTA0, FIG. 20C is a state of transmission and reception of a packet inthe communication station STA0, FIG. 20D is a state of transmission andreception of a packet in the communication station STA1, and FIG. 20E isa state of reception operation in the communication station STA1. Inaddition, a reception (Rx) activity level and a transmission (Tx)activity level in the communication station STA0 is shown on the upperside of FIG. 20A, and a reception (Rx) activity level and a transmission(Tx) activity level in the communication station STA1 is shown on thelower side of FIG. 20E. In this figure, a case where the transition ismade in accordance with a request from the communication station STA1 isreferred to as an example.

In an initial state of FIGS. 20A to 20E, the transmission and receptionof data is performed in a state where both the communication stationsSTA0 and STA1 are in the level 3 with respect to the transmission andreception levels relating to each other, and the transmission andreception of data is performed immediately when the transmission data isgenerated in the communication station STA0. However, in FIGS. 20A to20E, this transmission and reception of data is not performedfrequently, transmission and reception of data D19 is performed aftersome time elapsing from transmission and reception of data D18, and datais not transmitted further for a while. Then, the communication stationSTA1 decides to change the reception activity level relating to thecommunication station STA0 to the level 2 on the ground that thetransmission and reception of data is only performed dispersively inexcess of a permissible value. After that, the communication stationSTA1 notifies that “the STA1 changes the reception activity levelrelating to the STA0 to the level 2” in a beacon (B1-21) transmitted atthe beacon transmission timing thereof or in data (not shown in thefigure) transmitted immediately after that, and changes the activitylevel to the level 2 as notified. The communication station STA0 havingreceived this notice changes the transmission activity level relating tothe communication station STA1 to the level 2.

After the transition is made to the active level 2, a transmissiontrigger is generated in accordance with the procedure explained above,and transmission and reception of data is performed with thetransmission trigger as the start.

Although the communication station STA1 changes the activity level tothe level 2 on the ground that “the transmission and reception of datais only performed dispersively in excess of the permissible value” inthe above-described example, specifically, there is also a case wherethe change is made on the ground that “transmission and reception isonly performed with respect to the volume of data which even thereception active level 2 is capable of receiving”.

In addition, although the procedure of notifying that the activity levelis lowered is performed in the above-described example, there is also acase where this procedure is omitted. In this case, useless processingcan be omitted by setting the permissible value in the STA1 on thereception side higher than the permissible value in the STA0 on thetransmission side.

Further, although the communication station STA1 that is the receptionside decides that “the activity level is changed from the level 3 to thelevel 2” in the above-described example, there is also a case where thecommunication station STA0 that is the transmission side makes such adecision and the reception side follows this decision. Since a procedurein this case is similar to the procedure explained above, an explanationthereof is not specifically made here.

Network Broadcast

As explained above, the transmission and reception level in eachcommunication station is the level 0 in the state where the transmissionand reception of data is not performed, so that power is saved.

On the other hand, when broadcast information to be conveyed to thewhole network is transmitted, the transmission is sequentially performedin a form shown, for example, in FIGS. 21A, 21B, and 21C, and eachcommunication station conveys the received broadcast information toneighboring communication stations, so that the information istransmitted to all the communication stations in the network.

When broadcast information is transmitted and received in thetransmission and reception level 0, it is necessary to transmit themessage a plurality of times aiming at timing immediately aftertransmission of a beacon of each communication station, which iswasteful. In such a case where the broadcast information isconsecutively generated, traffic becomes increased which leads to awaste of band.

Broadcast Transmission and Reception Procedure

Accordingly, when broadcast information is generated, an operation statethereof is made into an ACT-1all, the transmission activity levelrelating to each communication station is changed while transmitting “arequest that the operation state is changed to the ACT-1all” to aneighboring communication station after the reception activity levelrelating to all the neighboring communication stations is set to thelevel 1, and the broadcast information is informed within a transmissionbeacon thereof or in a packet transmitted immediately after thetransmission of beacon until the transmission activity level registeredin the neighbor list becomes the level 1. Further, the operation statethereof is written in the transmission beacon and in the above-describedrequest information.

A specific example is shown in chronological order in FIGS. 22A to 22C.FIGS. 22A to 22C are diagrams showing an example of a transmission andreception procedure of broadcast information, and a case where thecommunication station STA0 conveys the broadcast information to thecommunication station STA1 and the communication station STA2 in such anarrangement of communication stations as shown in FIGS. 21A to 21C, forexample, is referred to as an example. FIG. 22A is a state oftransmission and reception of a packet in the communication stationSTA0, FIG. 22B is a state of transmission and reception of a packet inthe communication station STA1, and FIG. 22C is a state of transmissionand reception of a packet in the communication station STA2. Inaddition, an activity level of each of communication stations STA0,STA1, and STA2 is shown on the upper side of FIG. 22A.

FIG. 23 shows an operation state of each communication station and astate of the neighbor list in the example of each time in thechronological order in FIGS. 22A to 22C.

Each communication station is in the active level 0 at the time T0 thatis an initial state of FIGS. 22A to 22C, and only transmission of abeacon thereof and reception processing immediately after that over thelisten window (LT) are performed. At this time, all items in theneighbor list of each station are in the active level 0 (ACT-0) as shownin FIG. 23.

After that, broadcast information to be transmitted to the communicationstation STA0 arrives at the time T1. With this information as the start,the communication station STA0 sets the operation state thereof to theACT-1all, and sets the reception activity levels relating to allcommunication stations existing in the neighbor list to the level 1. Atthis point of time, the communication station STA0 has shifted into amode to receive a beacon of each communication station.

After that, the communication station STA0 transmits page informationaddressed to the communication station STA1 indicating that “it isdesired that the operation state is changed to the ACT-1all” afterreceiving a beacon transmitted by the communication station STA1 at thebeacon transmission time T2 of the communication station STA1. Thecommunication station STA1 acknowledges this request, and transmitsindication information indicating that “the operation state has beenchanged to the ACT-1all” at the time T3 as notified information (thatis, the destination address is made to a broadcast address). At thispoint of time, the communication station STA1 sets the operation stateto the ACT-1all, sets the reception activity levels relating to allcommunication stations existing in the neighbor list to the level 1, andalso sets the transmission activity level to the communication stationSTA0 that is a transmission source of the page information to the level1. Further, the transmission activity level relating to thecommunication station STA1 is set to the level 1 in the communicationstation STA0 having received the above-described indication informationtransmitted by the communication station STA1.

After that, it becomes the beacon transmission time of the communicationstation STA0 at the time T4. In the beacon, it is written that theoperation state of the communication station STA0 is set to theACT-1all. At this time, since the transmission activity level relatingto the communication station STA1 has been already set to the level 1,the communication station STA/D recognizes that the communicationstation STA1 performs reception, and transmits the broadcastinformation. This broadcast information is received by the communicationstation STA1. However, the communication station STA0 recognizes thatthe broadcast information is not distributed to the communicationstation STA2, because the transmission activity level relating to thecommunication station STA2 registered in the neighbor list thereof isthe level 0. Note that there is also a case where the communicationstation STA/D does not transmit the broadcast information until thetransmission activity levels relating to all communication stationsregistered in the neighbor list thereof become the level 1 or higher.

Further after that, the communication stations STA1 and STA0 transmitpage information addressed to the communication station STA2 indicatingthat “it is desired that the operation state is changed to the ACT-1all”after receiving a beacon transmitted by the communication station STA2at the time T5. In this figure, a case where the communication stationSTA0 transmits the page information is shown as an example. Thecommunication station STA2 acknowledges this request, and transmitsindication information indicating that “the operation state has beenchanged to the ACT-1all” at the time T6 as notified information in asimilar procedure to the one described above. At this point of time, thecommunication station STA2 sets the operation state to the ACT-1all,sets the reception activity levels relating to all communicationstations existing in the neighbor list to the level 1, and also sets thetransmission activity level to the communication station STA0 that isthe transmission source of the page information to the level 1. Inaddition, the communication stations STA0 and STA1 having received theabove-described indication information transmitted by the communicationstation STA2 set the transmission activity level relating to thecommunication station STA2 to the level 1.

After that, the communication station STA1 transmits a beacon at thetime T7. In the beacon, it is written that the operation state of thecommunication station STA1 has been set to the ACT-1all. At this time,in case that the broadcast information has been previously received fromthe communication station STA0, the communication station STA1 transmitsthe broadcast information. At this point of time, the broadcastinformation has been transmitted to the communication stations STA1 andSTA2. On the other hand, the communication station STA2 recognizes thatthe operation state of the communication station STA1 has been set tothe ACT-1all by receiving the beacon of the communication station STA1,and changes the transmission activity level relating to thecommunication station STA1 to the level 1.

After that, the communication station STA0 transmits a beacon at thetime T8, and also transmits the broadcast information, because thetransmission activity levels relating to all neighboring stations in thecommunication station STA0 are the level 1 at this point of time.

In such procedure as described above, each communication station canmutually change an operation state of a neighboring communicationstation to the ACT-1all. There is also a case where the changedoperation state is returned to the ACT-0 on the ground that receptiondata and the like do not exist over a certain period of time.

Information Written in Beacon

Explanation of writing an operation state in a beacon is made above;further details are explained with respect to information written in abeacon.

FIG. 24 is a diagram showing an example of a part of information writtenin a beacon in the present system. In the beacon, there exist at leastan address of transmission station (STA-ID), a field showing thereception time of a receivable beacon (NBOI), a field showing thereception time of a beacon to which reception is actually performed inthe reception active level 1 or higher (NBAI), and a field showing anoperation state of this communication station (Activity Status).

The address identifying the transmission station is written in theSTA-ID. The field showing the operation state of the communicationstation (Activity Status) is the field showing the operation stateexplained above, and any one of the following operation states is shown.

ACT-0all: One or more neighboring stations whose reception activitylevels are the level 0 exist.

ACT-1all: Reception activity levels of all the neighboring stations arethe level 1 or higher.

ACT-3all: Activity levels relating to one or more neighboring stationsare the level 3.

Activity Level Change Request Message

Although the explanation is made above with respect to the embodiment inwhich the communication station informs the communication partnerstation of the decision of making the transition of the activity levelthereof by a beacon signal, a procedure of changing an activity level inwhich transmission of a message other than a beacon signal is employedas a trigger is explained next.

A procedure in a case where a transition is made in a direction ofraising the activity level is shown in FIG. 25.

Although the activity level is the level 0 in a state where traffic doesnot exist, processing of raising an Activity of a link is started whentraffic addressed to another communication station is delivered to a MAClayer of a certain communication station. After that, the activity levelis raised as further traffic is delivered to the MAC layer on thetransmission side.

In FIG. 25, a case where a node #1 is a transmission source node of thetraffic and a node #2 is a destination node is referred to as anexample. As shown in this figure, an increase in the activity level isstarted by a trigger that is an instruction given from the transmissionsource. In the case where the transmission side wants the destinationnode to raise the activity level, a request message of “AL*_RQ” istransmitted after confirming that a Rx. active level from this node isthe level 1 or higher and notifies that the transmission side wants thedestination node to raise the activity level. When this request messageis received, the reception side sets a Rx. active level relating to thetransmission source node to the designated level, and returns a responsemessage of “AL*_CF” after further confirming that a Tx. active level isthe level 1 or higher and notifies the transmission source node that theactive level has been raised. When this response message is received,the transmission side sets the transmission active level relating to thedestination node to the designated level.

As shown in this figure, a similar procedure can be applied to thetransition in an upward direction to all the active levels.

The trigger to the transition to Active Level_0.fwdarw.Active Level_1 isthe generation of transmission data.

The trigger to the transition after that: Active Level_1.fwdarw.ActiveLevel_2.fwdarw.Active Level_3 may be started when the number of packetsexceeds a predetermined threshold value by monitoring the number ofpackets accumulated in the transmission buffer, for example.

Next, a procedure in a case where the transition is made in a directionof lowering the activity level is explained using FIG. 26.

Processing for lowering the activity level becomes necessary whentransmission and reception of the traffic is discontinued though theactivity level is raised. A timer is kept running to monitor time duringwhich there is no transmission and reception of the traffic, and theactive level is lowered by making the expiration of the timer as atrigger. At this time, it is necessary to set separately a timer tolower the Tx. active level and a timer to lower the Rx. active level, amargin is given by setting a time that is set to the timer to lower theTx active level shorter than the timer to lower the Rx. active level,and the generation of such useless traffic that “a receiving device hasnot received, though transmission is performed” can be prevented.

Further, as the processing at the time of lowering the active level, itis also conceivable to follow a procedure through exchanging messagessimilarly to the case of raising the active level. Even in this case, amechanism to lower the active level using the timer is required in orderto cope with the link in which the communication is suddenlydiscontinued.

It should be noted that an example of a configuration of a communicationapparatus which exclusively performs transmission and reception isexplained in the above described embodiment, however, it is alsopossible that a board, a card, and the like to perform communicationprocessing equivalent to the transmission unit and the reception unit ofthis embodiment are mounted on a personal computer apparatus performingvarious data processing, for example, and software is installed toexecute processing in a base-band unit by a central processing unit onthe computer apparatus side.

1. A communication apparatus configured to perform wirelesscommunication, the communication apparatus comprising: a receiverconfigured to operate in one of the at least three active levels relatedto power saving operations, each of the at least three active levelsspecifying a condition for operating the receiver, wherein at a firstactive level, the receiver operates for a designated time period aftertransmitting a beacon signal, at a second active level, the receiveroperates for a designated time period after transmitting the beaconsignal, and for a beacon receiving time period corresponding toreceiving a beacon signal from a different communication apparatus, at athird active level, at least one of a transmitter and the receiver iscontinuously operational.
 2. The communication apparatus according toclaim 1, wherein, when the different communication apparatus isoperating at the second active level, the transmitter transmits a datasignal based on receiving a reply signal, that the differentcommunication apparatus sends in response to receiving the beaconsignal.
 3. A communication apparatus according to claim 1, furthercomprising: a management unit configured to manage active levels forother communication apparatuses, wherein the active levels for the othercommunication apparatus differ among each of the other communicationapparatuses.
 4. The communication apparatus according to claim 1,wherein the communication apparatus enters a sleep state when no data isreceived within a predetermined time period.
 5. The communicationapparatus according to claim 4, wherein the communication apparatustransmits information indicating a current active level for thereceiver.
 6. The communication apparatus according to claim 4, whereinthe communication apparatus transmits information corresponding to achange of active level for the receiver.